This invention relates to air filters. In particular, it relates to electronically-enhanced filters that include a trapping medium.
Precipitator-type air filters of the type depicted in U.S. Pat. No. 2,593,869 to Fruth (1952) operate by first ionizing particulate-carrying air to charge dust contained therein, and then pass the air between oppositely charged, end-on aligned parallel plates to which the dust adheres. Such precipitating air cleaners are highly efficient when the plates are initially clean. However, performance drops off as the plates become covered with collected dust. Hence, regular cleaning is required to maintain efficiency. This cleaning operation for precipitator-type air cleaners is awkward and costly to effect.
An advantage of filters of the trapping media type is that such media may be readily removed and replaced once they are filled with dust.
It is known that in trapping airborne particles in disposable filter media such as fibrous matrices of glass, wool and the like, the trapping capacity of such filter media can be enhanced by ionizing the air, and charging the dust therein, before it enters the filter medium. U.S. Pat. Nos. 3,706,182 to Sargent (1972), and 4,244,710 to Burger (1981) both depict such an arrangement. In both of these references, ions are introduced into the airflow stream by ion emitters positioned at an upstream location in the airflow, at a spaced distance from the filter medium that is intended to trap and remove charged particles from the airflow. Prior inventions by the present inventor also rely on the upstream release of ions into an air flow as presented in U.S. Pat. Nos. 5,518,531 (1996) and 6,077,334 (Jun. 20 2000).
It is also known that the trapping of dust particles, especially charged dust particles, can be enhanced by using as a trapping medium an air-permeable matrix of non-conducting, polarizable material. Local dipoles formed within such medium help trap and bind dust particles. An example of a prior art reference based on this principle is U.S. Pat. No. 4,549,887, by the present inventor.
The present invention makes use of the airflow-aligned, charged parallel plate principle and, optionally, the ionization principle in conjunction with polarized media to provide an improved performance air filter.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.
In one aspect of the invention a series of generally parallel, alternately charged metal electrodes, aligned to receive air-flow are edge-on, used as polarizing electrodes to polarize trapping media contained between electrodes. The trapping medium may be in the form of a fibrous dielectric pad and/or may comprise pleated panels of air permeable trapping material. The electrodes are preferably aligned parallel to the airflow (although this is optional, to provide a polarizing, transverse field though the trapping medium. The polarizing electrodes may be in the form of plates between which the trapping media is placed. Alternately, polarizing electrodes may be formed right on the trapping media surface as by sheets of conductive screening or fabric. This can also be effected by rendering surface segments of the trapping media conducting as well as by providing air permeable conductive layer laid over such surfaces. The electrodes and trapping media may conveniently be formatted as a cartridge for ready removal and replacement.
In all of these variants, ionization may be provided upstream in the arriving airflow by a series of ionizing needles or other ionizing elements such as fine wires or conducting strings (c.f. U.S. Pat. No. 5,573,577, Nov. 12, 1996 by the present inventor). Such ionization charges dust particles in the air flow, enhancing further the trapping efficiency of the media present in the polarizing field formed between the oppositely charged polarizing electrodes.
Conductive surface portions may be formed on alternating sections of trapping medium constructed as a continuous surface folded into pleated panels by coating the medium with a conductive material, such as fine carbon or aluminum, preferably mixed with a binder. Conductive surfaces may also be formed by transferring conductive panels of conductive, porous (air-permeable) media to the trapping media as by an adhesive.
With trapping media contained between polarizing electrodes, a high potential voltage source is connected to provide a polarizing potential difference between consecutive electrodes. This potential difference not only tends to polarize the intervening portions of the trapping medium but also creates an electrical potential field between the electrodes with a high field gradient. Dust particles, particularly charged dust particles, are drawn laterally in the air flow by this transverse field to contact and be retrained in the trapping medium.
By these arrangements an improved air filter of increased efficiency and cost effectiveness is provided.
The foregoing summarizes the principal features of the invention and some of its optional aspects. The invention may be further understood by the description of the preferred embodiments, in conjunction with the drawings, which now follow.